一些範例：

0. 目錄File

遍歷目錄下的檔案

import java.io.File;  
import java.io.IOException;  
  
public class DirErgodic {  
  
    private static int depth=1;  
      
    public static void find(String pathName,int depth) throws IOException{  
        int filecount=0;  
        //獲取pathName的File物件  
        File dirFile = new File(pathName);  
        //判斷該檔案或目錄是否存在，不存在時在控制檯輸出提醒  
        if (!dirFile.exists()) {  
            System.out.println("do not exit");  
            return ;  
        }  
        //判斷如果不是一個目錄，就判斷是不是一個檔案，時檔案則輸出檔案路徑  
        if (!dirFile.isDirectory()) {  
            if (dirFile.isFile()) {  
                System.out.println(dirFile.getCanonicalFile());  
            }  
            return ;  
        }  
          
        for (int j = 0; j < depth; j++) {  
            System.out.print("  ");  
        }  
        System.out.print("|--");  
        System.out.println(dirFile.getName());  
        //獲取此目錄下的所有檔名與目錄名  
        String[] fileList = dirFile.list();  
        int currentDepth=depth+1;  
        for (int i = 0; i < fileList.length; i++) {  
            //遍歷檔案目錄  
            String string = fileList[i];  
            //File("documentName","fileName")是File的另一個構造器  
            File file = new File(dirFile.getPath(),string);  
            String name = file.getName();  
            //如果是一個目錄，搜尋深度depth++，輸出目錄名後，進行遞迴  
            if (file.isDirectory()) {  
                //遞迴  
                find(file.getCanonicalPath(),currentDepth);  
            }else{  
                //如果是檔案，則直接輸出檔名  
                for (int j = 0; j < currentDepth; j++) {  
                    System.out.print("   ");  
                }  
                System.out.print("|--");  
                System.out.println(name);  
                  
            }  
        }  
    }  
      
    public static void main(String[] args) throws IOException{  
        find("D:\\MongoDB", depth);  
    }  
}  
 

1.讀寫

try{  
    FileInputStream in=new FileInputStream("count.txt");  
    DataInputStream dataIn=new DataInputStream(in);  
    number=dataIn.readInt();  
    number++;  
    in.close();  
    dataIn.close();  
}  
catch(FileNotFoundException e){   
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    number++;  
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    try {FileOutputStream out=new  
    FileOutputStream("count.txt");  
    DataOutputStream dataOut=new  
    DataOutputStream(out);  
    dataOut.writeInt(number);  
    out.close();dataOut.close();  
}  
catch(IOException ee){}  
}  
catch(IOException ee)  
{  
}  
}  
else{  
    number++;  
try{  
    FileOutputStream out=new FileOutputStream("count.txt");  
    DataOutputStream dataOut=new DataOutputStream(out);  
    dataOut.writeInt(number);  
    out.close();dataOut.close();  
}  
    catch(FileNotFoundException e){}  
    catch(IOException e){}  
 }  
}  

2 按行讀

 try{
File f=new File("D:/test","A.txt");
FileReader in=new FileReader(f);
BufferedReader buffer=new BufferedReader(in);
String s=null;
while((s=buffer.readLine())!=null)
{ out.print(s+"<BR>");
}
in.close();buffer.close();
}
catch(IOException ee)
{out.print(" 檔案不存在");}